Method and Limitations

Color Management

The image Color Space is its input transform, often called an IDT. It converts stored values into the scene-linear working values used by the calibration. For example, Panasonic V-Log/V-Gamut footage requires the corresponding input transform from Blender’s active color configuration.

The display transform changes the preview without changing sampled values. Non-Color bypasses input conversion and is only appropriate for data intentionally encoded that way.

See Color Spaces in the Blender Manual.

Sampling Model

MacBlend supports two 24-patch chart models: the ColorChecker Classic (after 2014) and SpyderCheckr 24.

Patch Size determines how large the chart overlay patches are drawn. A value of 40 results in patches that are 40 × 40 pixels. Moving the corners introduces perspective, so the visible patch sizes change with the shape of the chart.

Target Data

The target can be either MacBlend’s generated reference values or a second sampled chart.

With Use reference values as target enabled, MacBlend uses the reference dataset for the image’s chart model and converts them into the selected linear Target Gamut. This produces 24 target RGB values used by the matrix fit.

With Use reference values as target disabled, Target selects another sampled image. The source and target images must contain the same chart model. This is useful when matching a photographed chart to another photographed chart rather than to the generated reference dataset.

MacBlend initially matches Blender’s File Color Space setting when possible. If no match is found, it reports the problem and uses Linear Rec. 709 as a fallback.

Note

For use in the current scene, Target Gamut should match the gamut selected under File Color Space.

Transform Direction

Forward : Transforms the sampled source toward the target.

Inverse : Transforms the target back toward the sampled source.

LUT exports contain both directions.

Normalization

Normalize separates a broad brightness difference before fitting the color matrix. The Neutral 5 patch and Rec. 709 luminance coefficients determine the scale.

Create Exposure Node represents that scale as an adjustable node after the matrix.

Limitations

A single RGB matrix cannot reliably repair an incorrect gamma, display rendering, clipped channels, local or selective grading, uneven lighting, glare, shadows, or chart damage. Built-in references assume D65 conditions; unusual illumination reduces the accuracy of a reference-based result.

Important

Check the result on both the chart and the rest of the image. Even when MacBlend completes the calculation, poor lighting, glare, clipped colors, or an incorrect image Color Space can produce a bad result.

Reference Data Sources

See Color Management in the Blender Manual for the target-gamut context.

See Also